248 THE VITAMINS 



carotene by ethyl oleate and the growth-promoting properties of pure 

 carotene. They were, however, unable to confirm the claims of v. Euler 

 that dihydro-a-crocetin shares with carotene the power to replace vita- 

 min A in the diet. 



Following the announcement of v. Euler et al. of the activity of 

 carotene as a source of vitamin A, Moore (1929) confirmed their 

 results and in a series of important studies obtained evidence which 

 appears to throw light upon the differences between vitamin A in plant 

 and animal materials and to mark an important advance in the chemistry 

 of this vitamin. In the preliminary note in which he first reported 

 the confirmation of v. Euler's results, Moore (1929) called attention 

 to the fact that the Japanese vitamin A concentrate biosterin was stated 

 by Takahashi et al. (1925), confirmed by Morton and Heilbron (1928) 

 to be characterized by marked selective absorption at 320 pifx, but no 

 absorption in the visible spectrum. Carotene on the other hand exhibits 

 selective absorption in the visible spectrum and no marked bands in 

 the ultra-violet region. In spite of these differences, the minimum 

 physiological dose for rats of each of the two materials appears to be 

 about the same, in the neighborhood of 0.005 milligram daily. In 

 endeavoring to reconcile these difficulties, Moore suggested two possi- 

 bilities : " ( 1 ) Both carotin and the classical 'vitamin A' may inde- 

 pendently possess the same physiological action or (2) physiological 

 action may be due to an inactive impurity present in each in amounts 

 so minute as not to affect the physical properties of the materials in 

 bulk." 



A few months later, however, Moore (1929b) reported preliminary 

 experiments suggesting the possibility that carotene, while not identical 

 with vitamin A, may be the precursor from which the vitamin is formed 

 in vivo. These experiments consisted briefly in feeding rats depleted of 

 their vitamin A reserves graded doses of carotene, from 0.0001 to 0.75 

 milligram daily, and after 36 days killing the rats and examining their 

 liver fats for carotene and for vitamin A by colorimetric and spectro- 

 graphic methods. 



It was noted first that although the largest amount of carotene 

 was sufficient to color the whole rat intensely yellow if absorbed un- 

 changed, the body fat was found to be as colorless as that of the 

 controls and the liver to show only feeble yellow pigmentation. On the 

 other hand, an intense blue color was given with antimony trichloride 

 and on spectrographic examination the absorption band was found to 

 be at 610 to 630 [lu, characteristic of vitamin A, rather than 590 [ifi 

 characteristic of carotene. A comparison of the blue and yellow units 



